1. Field of the Invention
The present invention generally relates to an interference detecting apparatus and a tomography apparatus using interference property of light and detecting a structure of a measurement sample.
2. Description of the Related Art
A shape measuring apparatus employing light interference tomography is known as a measuring apparatus by which an internal structure, a refractive index, a thickness and so forth of an object is obtained.
As such a shape measuring apparatus, there is one shown in FIG. 14 for example. In this shape measuring apparatus, light L 101 emitted from a light source having a short coherence distance is split into object light L102 and reference light L103 by a beam splitter 102. The object light L102 is reflected by a measurement sample S via a scanner 103, thus becomes object light L104, and is incident on the beam splitter 102 again. Further, the reference light L103 is reflected by a reference-light mirror 105 positioned by a motor 106 via a frequency shifter 104, and is incident on the beam splitter 102 again.
The object light L104 and reference light L103 are combined as a result of being incident on the beam splitter 102, and then is incident on a photodetector 107 as interference light L105. The photodetector 107 detects the interference light in which light intensity is modulated through interference between the object light L104 and reference light L103, and generates a detection signal. The detection signal undergoes filtering, A/D (analog to digital) conversion, for example, by a signal processing circuit 108, and is input to a control part 109. In the control part 109, based on the input signal, an image indicating an internal structure of the measurement sample S, for example, is generated as a measurement result. Further, the control part 109 drives the motor 106 while controlling a motor control circuit 110 based on the input signal and a feedback signal from the motor 106. Further, the control part 109 controls the scanner 103 so as to cause it to scan the surface of the measurement sample S with the object light L102.
In this shape measuring apparatus, the measurement sample S is moved along Z directions or a reference mirror 105 is moved along X directions, and a distance the measurement sample S or reference mirror 105 has moved is obtained. Thereby, a distribution in reflectance of the measurement sample S along depth directions is obtained. Thereby, the shape measuring apparatus can perform tomographic measurement of the measurement sample S, and thereby, measures an internal shape and an external shape of the measurement sample S. This shape measuring apparatus can be used for observation of the inside of a living body by using light of a wavelength range of red through near infrared, for example.
Further, by the shape measuring apparatus in the prior art, when pulse laser is emitted as the light source 101 having a short coherent distance, it is possible to observe an internal structure of the measurement sample S by using a component thereof for which interference occurs as a result of the pulse reflected by the reference mirror 105 being on time.
However, in the shape measuring apparatus in the prior art, as the light source 101 is of a single one normally, it is necessary to control interference by mechanically controlling the position of the reference mirror 105 along the X directions. However, in many cases, as the movement speed of the reference mirror 105 has a limit, much time is required for measuring the measurement sample S.
Further, in the prior art, a tomography apparatus to which a method called Optical Frequency Domain Reflectometry: OFDR) is applied is proposed. However, actually, it is necessary to cause the frequency of a used laser to sweep through a wide range, and, mechanical driving is used for this purpose.
Further, in the prior art, there is an example without employing mechanical driving, which has, however, a low resolution.
The present invention has been proposed in consideration of the above-described situation, and an object of the present invention is to provide a shape detecting apparatus and a tomography apparatus by which it is possible to measure a sample within a short time at a high resolution.
An interference detecting apparatus relating to the present invention solving the above-described problems, comprises: a light source emitting light having coherency; a first signal generating means generating a first signal having a frequency of f1; a first optical frequency comb generating means using the first signal provided from above-mentioned first signal generating means, modulating the light provided from the above-mentioned light source, and generating reference light having a sideband every interval of frequency f1 in the light provided from the above-mentioned light source; a second signal generating means generating a second signal having a frequency of f2; a second optical frequency comb generating means using the second signal provided from above-mentioned second signal generating means, modulating the light provided from the above-mentioned light source, and generating object light having a sideband every interval of frequency f2 in the light provided from the above-mentioned light source; a combining means combining the reference light provided from the above-mentioned first optical frequency comb generating means and the object light generated by the above-mentioned second optical frequency comb generating means and reflected by a to-be-measured object so as to generate interference light; and a detecting means controlling an interference timing between the reference light provided from the above-mentioned first optical frequency comb generating means and the object light provided from the above-mentioned second optical frequency comb generating means, by using a phase difference or frequency difference between the first signal and second signal, and detecting a change in light intensity of the interference light.
A tomography apparatus relating to the present invention, comprises: in order to solve the above-described problems, a light source emitting light having coherency; a first signal generating means generating a first signal having a frequency of f1; a first optical frequency comb generating means using the first signal provided from the above-mentioned first signal generating means, modulating the light provided from the above-mentioned light source, and generating reference light having a sideband every interval of frequency f1 in the light provided from the above-mentioned light source; a second signal generating means generating a second signal having a frequency of f2; a second optical frequency comb generating means using the second signal provided from the above-mentioned second signal generating means, modulating the light provided from the above-mentioned light source, and generating object light having a sideband every interval of frequency f2 in the light provided from the above-mentioned light source; a combining means combining the reference light provided from the above-mentioned first optical frequency comb generating means and the object light generated by above-mentioned second optical frequency comb generating means and reflected by a to-be-measured object so as to generate interference light; a first detecting means controlling an interference timing between the reference light provided from the above-mentioned first optical frequency comb generating means and the object light provided from the above-mentioned second optical frequency comb generating means, by using a phase difference or frequency difference between the first signal and second signal, and detecting a change in light intensity of the interference light; a scanning means scanning the to-be-measured object with a position of application of the object light provided from the above-mentioned second optical frequency comb generating means; a second detecting means detecting shape information of the to-be-measured object based on an interference detection result given by the above-mentioned first detecting means; and an image producing means producing an image representing the shape of the to-be-measured object by using a plurality of shape information sets of the to-be-measured object generated by the above-mentioned second detecting means as a result of above-mentioned scanning means scanning it.
Other objects and further features of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.